The present invention relates to a multiple-part oil control ring for a piston e.g. in an internal combustion engine, or a compressor.
A known construction of a ring of this type comprises an expander or spring ring and one or more lamellar rings or rails supported by the expander.
The composite ring is located in a groove in the piston and the expander is arranged to urge the rails both radially outwards against the cylinder wall and axially against the walls of the groove.
The expander may take many forms though one form frequently encountered comprises a ring formed by folding a flat strip with a series of alternate cut-outs along each edge to form a U-shaped channel section and subsequently bending the channel section into a generally U-sectioned ring.
In the motor industry, engine designers wish to reduce engine dimensions to improve car body profiles and to reduce engine weight. One way of achieving this is to reduce the engine block dimension in the direction of the engine cylinders, however, it is generally preferable to do so without affecting the cylinder capacity and compression parameters. This can be done by reducing the height of the piston, and indeed this is frequently an objective sought by piston designers.
One of the drawbacks of the folded-strip form of expander described above resides in the fact that its minimum axial thickness, in practice, tends to be quite large if it is to perform its spring/support function effectively.